Cold cathode electron discharge devices



April 16, 1957 M. J. COHEN COLD CATHODE ELECTRON DISCHARGE DEVICES FiledNov. 22, 1952 INVENTOR. RIIN .1 E UHEN JTI'ORNEY United, States PatentCOLD CATHODE ELECTRON DISCHARGE DEVICES Martin J. Cohen, Princeton, N. Jassignor to Radio Corporation of America, a corporation of DelawareApplication November 22, 1952, Serial No. 322,012

Claims. (Cl. 313-54) This invention relates generally to cold cathodeelectron discharge devices and particularly to new and improvedevacuated cold cathode discharge devices.

Previously, a number of cold cathode electron discharge devices such ascold cathode rectifiers, amplifiers, and the like have been proposed.Many of these devices are structurally complex. Moreover, for theiroperation, some of these devices require one or more of a gas-filledenvelope, a secondary emitter, and means for producing either highmagnetic or high electrostatic fields for ionizing the gas. A device ofthis general type is described in U. S. Patent No. 2,616,986, entitledCold Cathode Gas-Filled Amplifier Tube and granted to John H. Coleman onNovember 4, 1952.

While these devices generally are satisfactory, a simpler andadvantageous cold cathode device is desirable which requires no gaseousmedium or complicated structure associated therewith.

An object of the invention is to provide an improved and simplified coldcathode electron discharge device.

Another object of the invention is to provide an improved and simplifiedvacuum-type cold cathode electron discharge device.

Another object of the invention is to providean improved v-acuum-typecold cathode electron discharge device for rectifying or amplifyingsignals input thereto.

Another object of the invention is to provide an improved vacuum typecold cathode electron. discharge device useful for detecting nuclear orother high energy radiations.

A further object of the invention is to provide a new and improved coldcathode for use in devices of the type herein disclosed.

A further object of the invention is to provide a new and improvedphotoemissive cold cathode.

A still further object of the invention is to provide a new and improvedcold cathode device employing a radioactive isotope.

According to the present.invention a cold cathode electron dischargedevice is hereinafter disclosed and claimed which is operative in avacuum and does not require the use of magnetic or other deflectioncircuitry. One feature of the invention is directed to a cold cathodeelectron discharge device employing 'a photoemitter, initially activatedeither by dark current signals or by a light source, which cooperateswith a phosphor or scintillation crystal positioned in the travel pathof the liberated photoelectrons. These electrons are urged in thedirection of the phosphor by an accelerating field whereby the phosphoror crystal produces photons of light when bombarded by thesephotoelec'trons. The light emission induces the liberation of furtherelectrons from the photoemitter. Thus the cooperative action of thephotoemitter and the phosphor (or scintillator) results in aregenerative discharge which substantially re- (hides the impedance ofthe device. Another feature of the invention is directed to a novel coldcathode employing a radioactive isotope which cathode is especiallyuseful in a device of the type described above. The cathode by aphysical mixture of radioactive and scintillator 2,789,240 Cfi PatentedApr. 16, 1957 2 material or by a homogeneous scintillator crystal orsolid containing a radioactive nuclide -as-a constituent part of itsatom. 7

Other features and advantages of the invention will be described inconnection with the accompanying drawing in which:

Figure l is a schematic circuit diagram of a vacuumtype cold cathoderectifier, according to the invention;

Figure 2 is a schematic circuit diagram of a further embodiment of theinvention wherein signal amplification or radiation detection may beachieved;

Figure 3 is a schematic diagram of another embodiment of the inventionsimilar in part to apparatus illustrated in Figure 1 and employing anovel photocathode; and

Figure 4 is a modification of the photocathode shown in Figure 3.

Similar reference characters are applied to similar elements throughoutthe drawing.-

Figure I of the drawingshows a cold cathode rectifier device embodyingthe invention. An evacuated envelope, glass, for example, contains aphotoemitter 13 supported by a conductive support member 15. A secondconductive member 17 is spaced from the photoemitter 13 and supports, ona surface thereof facing the photoemitter 13, a material 19 whichproduces light emission when subjected to electron bombardment. Thephotoemitter '13 may comprise, for example, cesium antimonide or cesiumsilver oxide. The light emission material 19 is selected to be amaterial which produces photon energy within the, range of lightsensitivity of the photoemitter 13. This material 19 may be a phosphorsuch as zinc activated zinc oxide, calcium tungstate, zinc sulfide,cadmium sulfide, or alternatively a suitable scintillation crystal, suchas anthracene.

To achieve signal rectification one terminal of a source 21 of signals23 to be rectified is connected via lead 25 to the conductive member '17which supports the phosphor or crystal 19. The remaining source terminalis connected to ground potential. Initially electrons are liberated fromthe cathode 13 by some such phenomena as spurious dark current emissionwithin the envelope. in the time intervals during which signals 23 causesupport member 17 to swing to a potential positive with respect to thepotential of support member '15, an electric field is establishedbetween the support members 15 and 17 which causes electrons liberatedby the photoemitter 13 to be accelerated toward and bombard the photonemitting material 19. Material 19, in response to this electronbombardment, produces light emissions which further activate thephotoemitter 13 and cause additional electron emission therefrom and avoltage to be developed across a load resistor 27 connected between thephotoemitter support member 15 and ground.

The cooperative and cyclical action of the photoemitter 13 and thephoton emitter 19 result in a regenerative electron discharge within thedevice and a lowering of its effective impedance during these intervals.In inter vals during which signals 23 cause support 17 to swing to apotential negative with respect to the potential of support member 15 noaccelerating field is produced which results in electron bombardment ofmaterial 19, the spuriously emitted electrons produced by thephotoemitter 13 return to its surface, and the impedance of thedischarge device is high. Thus rectification is achieved since duringpositive potential swings of support member 17 electrons flow from thephotoemitter 13 to the support member 17 and the potential across loadresistor 27 swings positively; during negative potential swings ofsupport member 17 no electrons leave the photo emitter13 andthepotential developed cross resistor 27 is substantially zero.

The cascade discharge mentioned above may be controlled as desiredeither by suitable selection of a load resistor by choosing a phosphoror photoemitter which saturates in its light or electron emission at agivenpoint. Also,' in theevent that a more rapid build-up. of thecascadedischarge is desired a light source 29 external the envelope 11 maybeutilized to enhance electron emission from the photoemitter 13.

Figure 2 shows a cold cathode amplifier embodiment of the inventionhaving a cylindrical configuration. In this arrangement the photoemitter13 is supported on a conductive rod 15 and is surrounded by acylindrical conductive member 17 on the inside surface of which thephosphor or scintillator material 19 is disposed. Electrode 17 isconnected to a source of positive potential via a resistor 31. A controlelectrode 33, such as a mesh grid'or other structure, is positionedintermediate the photoemitter 13 and the phosphor 19 and is biasednegatively with .respect to the photoemitter support member '15 by abias battery 35.

In operation the bias potential applied to the device is selected sothat a moderate quiescent electron. current flows from the photoemitter13 to the support member 17. Input signals 37 to be amplified arecoupled from a source (not shown) through a coupling capacitor 39 andare developed across a grid leak resistor 41. These input signals 37modulate the electric field established within the device by thepositive potential applied to support 17 and cause the quiescentelectron current to be modulated. accordingly. During positive potentialswings of the control electrode 33 the device current increases .and theinstantaneous potential developed across resistor 31 is large.Conversely, during negative potential swings of the control electrodethe device current is reduced and the instantaneous potential developedacross resistor 31 is small. An external light source 29 may be utilizedin the event that spurious or other light emission is ineffective ininitially activating the photoemitter 13.

Although the above device has been illustrated and described as a triodcamplifier, it will be recognized that additional electrodes may be addedwhereby the device operates as a tetrode, pentode, or the like.

Figure 3 shows a further embodiment of the invention which is similar inpart to the apparatus described with respect to Figure l and includes anovel cold cathode. In this example the photoemitter support member andthe external light source 29, illustrated in Figures 1 and 2, may beomitted and replaced with a photon source 43 including a radioactiveisotope and a scintillation material. The photon source 43 may comprisea homogeneous scintillation crystal or a solid having a radioactivenuclide as a constituent atom thereof, for example, radioactive carbonin anthracene. Alternatively, the photon source may comprise a physicalmixture, as shown in Figure 4, comprising a plurality of radioactiveemitters 45 having a plurality of layers 47 of scintillation materialinterspersed with and in contact with the radioactive emitters. Theradioactive emissions excite the scintillator to produce photons oflight which, in turn, activate the photoemitter 13. The combination ofthe photon source 43 and the photoemitter 13 thus provide a new anduseful cold cathode especially adapted for use in a dediations. In thedevices of Figures 1 and 3, for example, a positive potential may beapplied to support members 4 17 to establish an electric field withinthe device. The ambient radiation then excites the phosphor orscintillator 19 to either initiate or enhance the cascade discharge ofthe device. In this instance the resistor 27 may be replaced with asuitable voltmeter or other device for indicating the intensity of theincident radiation. In the deviceof Figure 2 the light source 29 and theinput circuit capacitor 39 may be omitted and the device operated forradiation detection in the manner above described.

What is claimed is:

1. A cold cathode electron discharge device comprising, an evacuatedenvelope, at photoemitter contained within said envelope, a photonsource within said envelope for activating said photoemitter to produceelectron emission therefrom, said source including a scintillationmaterial and a radioactive isotope, an element spaced from saidphotoemitter and responsive to electron bombardment for producing lightemissions within the light sensitivity range of, said photoemitter, andan electrode responsive to a potential impressed thereon foraccelerating electrons emitted by said photoemitter to bombard saidelement, said bombarded element thereby producing light emissionscausing further electron emission from said photoemitter. 1

2. A cold cathode electron discharge device compris ing, an evacuatedenvelope, a photoemitter contained within said envelope, a photon sourcewithin said envelope for activating said photoemitter to produceelectron emission therefrom, said source including a homogeneousscintillation crystal having a radioactive nuclide as a constituenta'tom thereof, an element spaced from said photoemitter and responsiveto electron bombardment for producing light emissions within the lightsensitivity range of said photoemitter, and an electrode responsive to apotential impressed thereon for accelerating electrons emitted by saidphotoemitter to bombard said element, said bombarded element therebyproducing light emissions causing further electron emission from saidphotoemitter.

3. A cold cathode electron discharge device comprising, an evacuatedenvelope, a photoemitter contained within said envelope, a photon sourceWithin said envelope for activating said photoemitter to produceelectron emission therefrom, said source including alternateinterspersed layers of radioactive and scintillation materials, anelement spaced from said photoemitter and responsive to electronbombardment for producing light emissions within the light sensitivityrange of said photoemitter, and an electrode responsive to a potentialimpressed thereon for accelerating electrons emitted by saidphotoemitter to bombard said element, said bombarded element therebyproducing light emissions causing further electron emission from saidphotoemitter.

4. A cold cathode comprising, in combination, a photoemitter, and ahomogeneous scintillation crystal having a radioactive nuclide as aconstituent atom thereof for producing photons of light for activatingsaid photoemitter.

5. A cold cathode comprising, in combination, a photoemitter, and aphoton source including a plurality of radioactive emitters and aplurality of layers of scintillation material interspersed with and inphysical contact with said emitters, said radioactive emittersbombarding said scintillation materials with high energy emissions toproduce photons of light for activating said photoemitter.

References Cited in the file of this patent UNITED STATES PATENTS MaurerOct. 15, 1940

